Methods for stripping and modifying surfaces with laser-induced ablation

ABSTRACT

A coating removal apparatus removes a coating from a surface. The apparatus has a movable scanning head and scanning optics. The scanning head is movable in one dimension, and the scanning optics adjust in two dimensions to compensate for movement of the scanning head to implement long range scanning with a uniform scanning pattern. Further, a surface roughness is determined by measuring specular and scattered reflections at various angles. For composite surfaces, the apparatus utilizes UV laser radiation and a controlled atmosphere to remove coating and alter the chemical characteristics at the surface.

RELATED APPLICATIONS

This application claims priority of U.S. provisional application Ser.No. 60/919,707, filed Mar. 22, 2007, and entitled “Preferred Methods forStripping and Modifying Surfaces with Laser-induced Ablation,” by thesame inventors. This application incorporates U.S. provisionalapplication Ser. No. 60/919,707, filed Mar. 22, 2007, and entitled“Preferred Methods for Stripping and Modifying Surfaces withLaser-induced Ablation” in its entirety by reference.

This application also claims priority of U.S. provisional applicationSer. No. 60/958,737, filed Jul. 9, 2007, and entitled “Apparatus andmethod for Ultraviolet Laser Surface Treatment of Composite Materials,”by a common inventor. This application incorporates U.S. provisionalapplication Ser. No. 60/958,737, filed Jul. 9, 2007, and entitled“Apparatus and method for Ultraviolet Laser Surface Treatment ofComposite Materials” in its entirety by reference.

FIELD OF THE INVENTION

The invention relates to ablating a coating using a laser. Inparticular, the invention relates to removing a coating from a surfaceusing a laser and light sensing system.

BACKGROUND OF THE INVENTION

Delivery of certain wavelengths of radiant energy is facilitated bytransmission along flexible silica fibers. The energy is dispersed fromthe emitting end of an optical fiber in a widening cone. The energyintensity is generally symmetric about the central fiber axis (e.g.,uniformly distributed in azimuth) at the emitting end. The distributionof emitted energy orthogonal to the azimuth angle is highly non-uniform,with highest intensity at the central axis, rapidly decreasing withincreasing divergence angle relative to the central fiber axis,sometimes approximated by a power cosine function of the divergenceangle.

Energy beam guiding structures are known that use refractive media (e.g.optical lenses) in combination with movable reflective media (e.g.mirrors) to focus and direct diverging radiant energy disposed aroundthe input beam axis to a target of interest. The optical lensestypically convert (collimate) the dispersing radiant energy to a secondbeam with the radiant energy directed more parallel to the input beamaxis. The second beam's energy is distributed over a cross-sectionalarea defined on a target surface oriented in a transverse planeintersecting the optical axis of the second beam. The size of thedefined area is typically limited by the diameter of the lenses. Themovable reflective media are coupled to transporting mechanisms and arepositioned to modify the direction of the collimated beam as a functionof time, typically in a raster pattern scan mode. The dynamicpositioning of the reflective media is generally arranged so that theenergy of the second beam, averaged over a multiple number of scancycles, is distributed as a less intense, more uniform energy intensitydistribution over the desired target surface area. In addition, one ormore condensing (focusing) lens can be used to focus the collimated beamenergy to a fine point at the target's surface. Combinations of mirrors,prisms, and/or lenses are used to achieve both effects. The typicalobjective of these combined reflective and refractive elements is tomodify the intensity distribution of the beam over the width of alimited transverse area and to move the scan area over a target surfaceto produce a less intense, more uniform, energy intensity distributionover a larger area.

In previous laser scanning heads, the beam is typically reflected fromtwo raster scanning mirrors movably mounted in a housing where they aredisposed with the first minor intercepting the input beam, reflecting itto the second minor, which then reflects the beam toward the target. Inother previous laser scanning heads, the beam is refracted throughmoving optical components to direct the beam toward the target.

Laser-based coating removal systems use pulses of light from high powerlasers to ablate or vaporize the paint or other coating from a surface.Each pulse removes the coating from a small region, typically 0.1 to 100square mm. The laser is pointed to a different area after each pulse,where the removal process is repeated until the entire surface iscleaned.

An advantage of lasers for coating removal is that each laser pulseremoves a predictable portion of the thickness of the coating, in thesmall region impacted by the pulse. This opens the possibility ofselective stripping where, for example, the topcoat could be removed butnot the primer.

In an attempt to provide uniform removal of the coating, the beam isscanned over the surface in a controlled manner. However, currentscanning head configurations and methods of removing the coating provideonly limited success in achieving uniform coating removal.

Further, current laser-based coating removal techniques are lesseffective when applied to newer composite materials, such asfiber-reinforced polymer composites. The use of fiber-reinforced polymercomposites in a variety of modern products highlights significanttechnical advantages that these materials exhibit. In comparison tometals and conventional plastics, composites have highstrength-to-weight ratios, high elastic modulus, and are very durable.For these reasons, composite materials have been employed in anincreasing number of demanding automotive, sports equipment, andaerospace applications. Composite materials have also demonstratedsignificant advantages in military “stealth” aircraft applications wherelight weight, structural efficiency and compatibility with“low-observables” (LO) coating systems are critical.

Composite materials have also been employed in commercial aircraftapplications, including fuselage and wing fairings, stabilizers, rudderstructures, and fuselage access hatches. In some applications, wide-bodyaircraft employ carbon fiber-reinforced plastic (CFRP) composite as theprimary load-bearing material in the fuselage and wing structures. Theuse of composite materials confers a number of performance advantages incomparison to all previous generations of commercial (metal) aircraft,notably including exceptional gains in fuel efficiency.

The CFRP-type composite material employed in aerospace applications isprocessed and fabricated with entirely different methods than thetraditional riveted aluminum structure that has previously dominatedairframe construction. The basic CFRP composite material is manufacturedby encapsulating directionally oriented carbon fibers with an epoxy-typeresin. Typically, woven carbon fiber “tapes” or “pre-forms” arepositioned over form tools or mandrels and are subsequently infused withthe epoxy resin using vacuum-assisted methods. The entire assembly isthen subjected to heat and pressure in an autoclave vessel in order tocure the epoxy resin under controlled conditions.

This technology allows manufacturers to fabricate complex airframestructures from multiple composite pieces including skins, bulkheads,stiffening ribs, stringers, and doubler plates. The heat and pressuregenerated by the autoclave process facilitates high-strength adhesivebonds between these various composite pieces as the complete assembly isfabricated. This allows the manufacturer to build large, complexcomposite structures that essentially function as a single piece.

Although composite materials provide technical advantages in a varietyof applications, manufacturers have had to confront several problems infabricating useful products at an acceptable cost. These problemsinclude the cleanliness and surface chemistry of the composite material.In most composite manufacturing processes, mold release agents andambient hydrocarbon aerosols are deposited on the composite surface asundesirable contaminants. These contaminants degrade the mechanicalproperties of adhesive bond joints as well as the adhesion of coatingson the composite surface. It is well known to those skilled in the artthat surface cleanliness and surface chemistry are critically importantto achieving consistent adhesive bonds as well as the adhesion ofhigh-performance coatings that extend the life of composite structuresin operational service.

Conventional approaches to aerospace composite surface cleaning andsurface preparation include hand-applied abrasive media and media-blasttechniques using a solvent rinse. These methods employ abrasive media toabrade the surface and thereby remove contaminated matrix material fromthe composite surface. In addition to being inherently labor-intensive,the use of abrasive processes for composite surface preparation entailsother disadvantages, including unintended damage to the compositesubstrate, substantial variability in process outcome that is difficultto control, large waste streams, and difficulty in thoroughly cleaningthe abrasive-treated substrate.

Aerospace and laser manufacturers have attempted to use laser-basedprocesses for surface treatments of composite materials, but thesedevelopments have not proven to be successful. A fundamental problem inthis regard is the fact that the infrared (IR) lasers employed in theseprocesses are not well suited to coating and bonding pre-treatments ofcomposite materials. Although IR lasers are used for most industrialcutting, welding, and coating removal applications, the infraredradiation they produce is readily transmitted through the epoxy matrixof many composite materials. This means that IR lasers cannot readilyproduce the closely controlled laser effects in a very shallow layer ofthe substrate surface that are required for coating and bondingpre-treatments of aerospace composites.

Conventional laser-based coating removal techniques are also limited intheir ability to accommodate certain surface preparation requirements.In preparing a surface for paint, for example, some applications requirethat, in addition to being clean, the surface should have a texture.That is, some paint sticks better if the surface is not perfectly flat.Lasers are capable of creating small divots in the surface that enhancepaint adhesion. The difficulty is in controlling the degree of surfaceroughness induced by the laser and determining if a desired surfaceroughness has been achieved.

SUMMARY OF THE INVENTION

Embodiments of the present invention are directed to a coating removalapparatus for and a method of removing a coating from a surface. Thecoating removal apparatus includes a laser path, an illumination path,and a reflected light path. Laser light is provided from a laser sourceto the surface via the laser path. Light to illuminate the surface isprovided from one or more illuminators to the surface via theillumination path. Reflected light resulting from the light illuminationimpinging the surface is directed from the surface to a photosensitivedetector via the reflected light path. In some embodiments, laserscanning optics also function as the illumination path for the lightillumination directed onto the surface. In other embodiments, theillumination path is separate from the laser path. The lightillumination is reflected off the surface and collected by thephotosensitive detector to achieve a known correspondence between thescanning optics conditions and the local surface color and/or textureparameters.

Each laser pulse generated by the laser source is directed by scanningoptics to a predetermined position on the coated surface. Where thelaser pulse impinges the position, the coating at the position isablated. The scanning optics are then adjusted to direct subsequentlaser light to other positions on the surface according to apredetermined pattern. The exact pattern of the coating to be removedcan be any desired pattern. Control logic within the apparatusdetermines the desired pattern according to a stored algorithm orprogram. Control signals are sent to the scanning optics, which includevarious optical elements and actuating means for moving some or all ofthese elements, thereby controlling the direction of the laser lightonto the surface.

In some embodiments, the coating removal apparatus is configured with amovable scanning head that includes the scanning optics. In someembodiments, the scanning head is movable in a first direction, forexample the y-direction relative to the surface, and the scanning opticsare configured to move in two directions, for example the y-directionand also the x-direction relative to the surface. Such a configurationenables a long range scanning path in the first direction correspondingto the scanning head movement, while implementing a uniform coatingremoval pattern.

In some embodiments, the coating removal apparatus is configured toremove coating to achieve a desired surface roughness. The surfaceroughness is measured in situ, in real-time as the coating removalprocess occurs. A roughness measuring laser source provides a laserlight to the surface, thereby generating laser specular reflection andscattered reflections. The magnitude of the reflections at variousangles are detected and measured. The measured results are used tocalculate the surface roughness.

In some embodiments, the surface is composed of materials and/orstructures that infrared (IR) laser light used to remove coatings merelypasses through without the desired effects. When the surface to beremoved is composed of such materials and/or structures, the coatingremoval apparatus includes an ultraviolet (UV) laser system. UV laserlight interacting with the surface causes photoablation effects. Sucheffects essentially vaporize a volume of the surface material as agaseous flow or a low-temperature plasma.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an exemplary block diagram of a coating removaldevice according to an embodiment of the present invention.

FIG. 2 illustrates an exemplary block diagram of a coating removaldevice according to another embodiment of the present invention.

FIG. 3 illustrates a coating removal device according to anotherembodiment of the present invention.

FIG. 4 illustrates a block diagram of a coating removal device accordingto yet another embodiment of the present invention.

FIG. 5 illustrates the coating removal system including an exemplaryconfiguration of the scanning optics.

FIG. 6 illustrates a top down view of a simplified block diagram of ascanning head including a single-axis laser scanner.

FIG. 7 illustrates an expanded view of a portion of the scanning patternshown in FIG. 6.

FIG. 8 illustrates the position of the laser scanner of FIG. 6 versustime.

FIG. 9 illustrates a top down view of a simplified block diagram of ascanning head including two single-axis laser scanners.

FIG. 10 illustrates an expanded view of the scanning pattern performedby the scanning head of FIG. 9.

FIG. 11 illustrates the position of the two laser scanners of FIG. 9versus time.

FIG. 12 illustrates a top down view of a simplified block diagram of ascanning head including two single-axis laser scanners.

FIG. 13 illustrates an expanded view of a portion of the scanningpattern performed by the scanning head of FIG. 12.

FIG. 14 illustrates the position of the two laser scanners and scanninghead of FIG. 12 versus time.

FIG. 15 illustrates an exemplary block diagram of the coating removaldevice of FIG. 1 including a gas flow delivery system.

FIG. 16 illustrates an exemplary block diagram of the coating removaldevice of FIG. 1 including a gas flow delivery system and controlled gaschamber.

FIG. 17 illustrates an exemplary application of a surface roughnessmeasuring scheme.

Embodiments of the coating removal device are described relative to theseveral views of the drawings. Where appropriate and only whereidentical elements are disclosed and shown in more than one drawing, thesame reference numeral will be used to represent such identicalelements.

DETAILED DESCRIPTION OF THE PRESENT INVENTION

Embodiments of the coating removal apparatus utilize various opticspaths to provide laser pulses to a coated surface, to direct a lightillumination to the coated surface, and to direct the reflected lightfrom the coated surface to a photosensitive detector and analyzer. Insome embodiments, the apparatus is an integrated device including alaser source, a beam splitter, scanning optics including actuating meansfor adjusting the scanning optics, a waste removal apparatus, one ormore light illuminators, a photosensitive detector, a comparator, and acontrol logic circuit. In other embodiments, the apparatus is dividedinto separate components, such as a head component and a body component,each of which is coupled via fiber optic cables and/or power lines.

FIG. 1 illustrates an exemplary block diagram of a coating removaldevice according to an embodiment of the present invention. The coatingremoval device 10 is an integrated device that includes a laser source12, a beam splitter 14, scanning optics 16, illuminators 18, aphotosensitive detector 20, a comparator 22, a control logic circuit 24,and a waste collector 26. Within FIG. 1, the solid lines betweenelements represent optical paths and the dashed lines represent datasignal paths. The laser source 12 generates a laser pulse, representedas light 30. Light 30 passes through the beam splitter 14 to thescanning optics 16. Within the scanning optics 16, the light 30 isaligned and focused such that the light 30 impinges a specific position52 on a coated surface 50. A laser path is defined as the path the laserpulse traverses to reach the coated surface 50. In reference to FIG. 1,the laser path includes the path through the beam splitter 14 and thescanning optics 16.

As is well known in the art of laser optics, a surface area of theposition 52 onto which the light 30 impinges can be made as small or aslarge as necessary to perform the desired functionality of ablating thecoating at the position 52. Increasing or decreasing the impingingsurface area respectively decreases or increases the light intensitydelivered onto the surface area. The amount of light intensity is anadjustable parameter which is used to meet various applicationspecifications. It is understood that the light intensity delivered overa given surface area depends not only on the given surface area but alsoin part to the laser source specifications and loss within theintegrated apparatus.

Upon impinging the position 52, the light 30 ablates a portion of thecoating corresponding to the position 52. It is anticipated that eachlaser pulse removes a uniform amount of coating. The amount of coatingremoved includes the surface area impinged by the light 30 and a depthof the coating at the position 52. An anticipated depth can becalculated based on the intensity of the light 30, the surface areaimpinged, the nature of the coating, etc. In operation, the actual depthof the coating that is removed can vary from the calculated depth.Underneath the coating to be removed is either a different coating (anundercoating) comprising a different material or a different color, orthe original surface material to which the coating was originallyapplied. In either case, it is anticipated that the undercoating ororiginal surface reflects a wavelength of light different than thatreflected by the coating being removed. As such, it can be determined ifthe coating to be removed is in fact completely removed by measuring awavelength of light reflected off the position 52. The illuminators 18provide a light illumination 32 to the position 52 on the coated surface50. Light illumination 32 is reflected off the position 52 as reflectedlight 34 and through the scanning optics 16 to the beam splitter 14. Atthe beam splitter 14, the reflected light 34 is split, or re-directed,from the laser path as re-directed reflected light 36. The light 36 isdirected to the photosensitive detector 20 where characteristics of thereflected light are measured. Data corresponding to the measuredcharacteristics is sent from the photosensitive detector 20 to thecomparator 22 via a data line 40.

An illumination path is defined as the path the light illuminationtraverses from the illuminators 18 to the surface 50. In reference toFIG. 1, the illumination path is independent of laser path.

A reflected light path is defined as the path the reflected lighttraverses from the coated surface 50 to the photosensitive sensor 20. Inreference to FIG. 1, the reflected light path includes the path throughthe scanning optics 16 and the beam splitter 14. In the coating removaldevice 10, the reflected light path includes the optics that comprisethe laser path.

The comparator 22 compares the measured characteristics of the reflectedlight to previously defined parameters and thresholds. The previouslydefined parameters and thresholds can be internally stored within thecomparator 22, or they can be received from a separate memory for thepurposes of being used in the comparison operation. The memory is aconventional memory type located within the integrated device 10.Included within the previously defined parameters are characteristics ofthe coating to be removed, for example the coating color.

The results of the comparison made by the comparator 22 are sent to thecontrol logic circuit 24 via a data line 42. The comparison determinesif the coating is sufficiently removed from the position 52. To makethis determination, the wavelength of the reflected light is measured.The reflected light wavelength indicates a color of a top layer of thecoated surface 50 at the position 52 after the portion of coating hasbeen ablated by the impinging light 30. If this measured top layer coloris substantially the same as a color of the coating to be removed, asdefined by the stored coating parameters, then it is determined that aportion of the coating to be removed still remains at the position 52.In this case, the laser pulse is then fired at this position and thesystem then moves to the next position. This process is repeated for anarea until a predetermined percentage of the positions within the areado not require the laser to fire. In this case, the system then moves tothe next area.

If the comparison performed by the comparator 22 determines that the toplayer color is substantially different than the previously definedcoating color, then it is concluded that directing another laser pulseonto the position 52 is not necessary. To move to the next position onthe surface, the control logic circuit 24 sends a control signal to thescanning optics 16 via a data line 44. The control signal instructs thescanning optics 16 to realign such that a subsequent laser pulse isdirected to a position on the coated surface 50 different than theposition 52. After the scanning optics 16 are realigned to a subsequentposition, a determination is then made as to whether or not the laserpulse should be fired at the new position.

Although not shown in the figures, individual optical elements withinthe scanning optics 16 are aligned using any conventional actuatingmeans for physically moving one or more of the individual opticalelements. For example, drive gears are connected to the optical elementsand a motor is connected to the drive gears. In this example, controlsignals sent by the control logic circuit 24 to the actuating means, thecontrol signals provide instructions as to the movement of the drivegears using the motor. Additional actuating means can also be includedto move the coating removal device 10 relative to the surface 50. Theadditional actuating means are under the control of the control logiccircuit 24 or other control logic circuit working in unison with thecontrol logic circuit 24.

The waste collector 26 collects the waste byproduct resulting from thelaser pulse impinging the coated surface 50 and ablating the top layercoating. The waste collector 26 includes a local storage for storing thecollected ablated waste byproduct. An alternative waste collector actsas a waste removal apparatus and is coupled to an external wastereceptacle such that the collected waste byproduct is transported to theexternal waste receptacle.

Illumination, as provided by the illuminators 18, and detection of theresulting reflected light, as performed by the photosensitive detector20, can be accomplished in several different manners. The illuminatorscan be comprised of one to many individual illuminators that provideillumination from a single wavelength to a wide range of wavelengths.Similarly, the photosensitive detector 20 can comprise one to manysensors for detecting light. One method using a single sensor with awide spectrum illuminator, constitutes a grayscale sensor that measuresthe relative lightness of a surface. Another method uses aspectrophotometer sensor that measures a reflectance at hundreds ofdifferent wavelengths. The use of multiple sensors allows the sensing tocompensate for variations in the tilt of the surface being ablated.Multiple sensors can also be combined with multiple wavelengths. In someembodiments, two color illumination and sensing is implemented where thetwo colors are red and blue. In this case, the configuration of theilluminators 18 includes two red illuminators and two blue illuminators.Alternatively, more or less than two illuminators can be used. In someembodiments, one or more red illuminators, one or more blueilluminators, and one or more green illuminators are used. It iscontemplated that any illumination and sensing techniques can be usedthat enables the coating removal system to determine the color of a toplayer of a coated surface.

The illumination colors can be separated using any conventionaltechnique. One approach uses filters within the photosensitive detectorsuch that the filters separate the colors and send each separated colorto a corresponding sensor. Another approach is to separate the colorsusing a grating. In yet another approach, color separation is performedusing a single sensor within the photosensitive detector 20 andseparating the colors temporally. To accomplish this in the case of redilluminators and blue illuminators, the red illuminators are energizedand the corresponding reflected light is measured by the sensor in thephotosensitive detector 20. Then, the blue illuminators are energizedand the corresponding reflected light is measured by the same sensor.The order can be reversed such that the blue light is measured prior tothe red light.

FIG. 1 shows an exemplary configuration in which the laser path and thereflected light path share common elements, and the illumination path isindependent of both the laser path and the reflected light path.Alternative path configurations are also contemplated.

FIG. 2 illustrates an exemplary block diagram of a coating removaldevice according to another embodiment of the present invention. Thecoating removal device 400 provides a similar function as the coatingand removal device 10 (FIG. 1), however, the coating removal device 400is configured such that the light illumination is directed through thescanning optics and the reflected light is collected directly from thecoated surface. The coating removal device 400 is an integrated devicethat includes a laser source 412, a laser minor 406, scanning optics416, one or more illuminators 418, a mirror 404, a photosensitivedetector 420, a comparator 422, a control logic circuit 424, and a wastecollector 426. The laser source 412 operates similarly as the lasersource 12 (FIG. 1) to generate a laser pulse, represented as light 430.Light 430 is reflected off the laser minor 406 to the scanning optics416. Within the scanning optics 416, the light 430 is aligned andfocused such that the light 430 impinges a specific position, such asthe position 52, on the coated surface 50. In reference to FIG. 2, thelaser path includes the laser minor 406 and the scanning optics 416.Upon impinging the position 52, the light 430 ablates a portion of thecoating corresponding to the position 52.

The illuminators 418 provide a light illumination 432 to the position 52on the coated surface 50. Light illumination 432 is reflected off theposition 52 as reflected light 434. The reflected light 432 is collectedby the photosensitive detector 420 where characteristics of thereflected light are measured. Data corresponding to the measuredcharacteristics is sent from the photosensitive detector 420 to thecomparator 422 via a data line 440.

In reference to FIG. 2, the reflected light path is the path from thesurface 50 of the photosensitive detector 420, and the illumination pathincludes the illuminators 418, the mirror 404, the laser mirror 406, andthe scanning optics 416. In the coating removal device 400, the laserpath and the illumination path share common elements, the laser minor406 and the scanning optics 416, and the reflected light path isseparate from the laser path and the illumination path.

The comparator 422 operates similarly to the comparator 22 (FIG. 1). Theresults of the comparison made by the comparator 422 are sent to thecontrol logic circuit 424 via a data line 442.

Although not shown in the figures, individual optical elements withinthe scanning optics 416 are aligned using any conventional actuatingmeans for physically moving one or more of the individual opticalelements. For example, drive gears are connected to the optical elementsand a motor is connected to the drive gears. In this example, controlsignals sent by the control logic circuit 424 to the actuating meansprovide instructions as to the movement of the drive gears using themotor. Additional actuating means can also be included to move thecoating removal device 400 relative to the surface 50. The additionalactuating means are under the control of the control logic circuit 424or other control logic circuit working in unison with the control logiccircuit 424.

The waste collector 426 collects the waste byproduct resulting from thelaser pulse impinging the coated surface 50 and ablating the top layercoating. The waste collector 426 operates in a manner similar to that ofthe waste collector 26 (FIG. 1).

FIG. 3 illustrates a coating removal device 700 according to anotherembodiment of the present invention. The coating removal device 700 isan integrated device that includes the laser source 412, the lasermirror 406, scanning optics 716, the one or more illuminators 418, themirror 404, a beam splitter 704, the photosensitive detector 420, thecomparator 422, the control logic circuit 424, and the waste collector426. The coating removal device 700 provides a similar function as thecoating and removal device 400 (FIG. 2), except that the coating removaldevice 700 is configured such that the reflected light 734 from thesurface 50 is directed back through the scanning optics 716. Thereflected light 734 is then redirected by the beam splitter 704 to thephotosensitive detector 420. In reference to FIG. 3, the laser pathincludes the laser minor 406, the beam splitter 702, and the scanningoptics 716. The reflected light path is the path from the surface 50 tothe photosensitive detector 420, including the scanning optics 716 andthe beam splitter 702. The illumination path includes the mirror 404,the laser mirror 406, the beam splitter 702, and the scanning optics716. In the coating removal device 700 of FIG. 3, the reflected lightpath, the laser path, and the light illumination path all include thescanning optics 716.

The exemplary configurations shown in FIGS. 1-3 include the coatingremoval apparatus as a single integrated device. It is alternativelycontemplated that the coating removal device includes separatecomponents coupled together, for example a head component and a bodycomponent. One such configuration is illustrated in FIG. 4, including ahead component 310 coupled to a body component 320. A coating removaldevice 300 function similarly as the coating removal device 10 of FIG. 1except that the beam splitter 14, the photosensitive detector 20, thecomparator 22, and the control logic circuit 24 are located in the bodycomponent 320, and the scanning optics16 are located in the headcomponent 310. The control logic circuit 24, located in the bodycomponent 320 sends control signals to the scanning optics 16 in thehead component 310 via data line 330. Focusing optics 322 are includedin the body component 320 to focus the light 30 into a first end of thefiber optic cable 116. The focusing optics 322 also direct the reflectedlight 34 received from the fiber optic cable 116 to the beam splitter14. The head component 310 includes a waste collector 112 that iscoupled to a waste receptacle 124 in the body component 320 via wastetransport tube 114.

Alternative configurations to the coating removal device 300 are alsocontemplated. For example, the laser source and waste receptacle can beincluded in the body component, and the remaining elements are includedin the head component. As with the single integrated deviceconfigurations, the head component and body component configurations canalternatively be configured such that the reflected light path isseparate from the laser path and the illumination path includes commonelements as the laser path, or the laser path, the illumination path,and the reflected light path all share common elements.

Numerous different optical configurations can be used within thescanning optics 16, 416, 716 (FIGS. 1-3) to direct the light 30, 430 tothe coated surface 50 and to direct the reflected light 34, 434, 734from the coated surface 50 to the photosensitive detector 20, 420. Anycombination of focusing optics, reflecting scanners, refractingscanners, beam splitters, or other conventional optical elements can beused. It is understood that the scanning optics have the ability to beoptically configured in any number of different configurations, usingany number of optical elements, such that the scanning optics 16 directa laser light pulse from a first optical position (such as the beamsplitter 14) to the coated surface and direct a reflected light from thecoated surface back to the first optical position.

FIG. 5 illustrates the coating removal system 700 including an exemplaryconfiguration of the scanning optics 716 (FIG. 3). The scanning optics716 include focusing optics 708, such as a telecentric scanning lens,reflecting scanners 704 and 706, and actuating means 710. The light 430is reflected by the reflecting scanners 704 and 706 to the focusingoptics 708. The focusing optics 708 direct and focus the light 430 to aposition, such as position 52, on the coated surface 50. The exactposition on the coated surface 50, and the dimensions of the lightimpinging the coated surface 50, are determined by the alignments of thescanning optics 708 and the reflecting scanners 704 and 706, which arealigned by the actuating means 710. The actuating means 710 includes anyconventional means for properly aligning each of the optical elementswithin the scanning optics 716, including but not limited to drive gearsand a motor. The actuating means 710 is controlled by control signalssent by the control logic circuit 424. The actuating means 710 can alsoinclude additional actuating means to move the coating removal device700 relative to the surface 50. The additional actuating means are underthe control of the control logic circuit 424 or other control logiccircuit working in unison with the control logic circuit 424. Althoughthe focusing optics 708 are shown in FIG. 5 as single elements, itshould be clear to those skilled in the art that the focusing optics 708can comprise one or more optical elements. Similarly, although tworeflecting scanners 704 and 706 are shown in FIG. 5, it should be clearthat more, or less than two reflecting scanners can be used. It shouldalso be clear that other types of optical elements can be used inaddition to or instead of the optical elements shown in FIG. 5.

The scanning optics direct and focus the laser light to a position, suchas position 52, on the coated surface 50. The exact position on thecoated surface 50, and the dimensions of the light impinging the coatedsurface 50, are determined by the alignments of the optical elementswithin the scanning optics, which are controlled by control signals sentby the control logic circuit.

As described in detail above, each laser pulse generated by the lasersource is directed to a predetermined position on the coated surface.After the coating is removed from a first position, the control logiccircuit instructs the focusing and scanning optics to align themselvessuch that a subsequent laser pulse is directed to a second positiondifferent than the first position. The control logic circuit determinesthe desired coating removal pattern according to a stored algorithm orprogram. In order to provide uniform removal of the coating, the laserpulses are scanned in a controlled uniform manner. Several method areused to provide uniform removal of the coating.

A scanning head is defined as that part of the coating removal devicethat includes the scanning optics used to direct the laser light ontothe surface. In the exemplary configurations shown in FIGS. 1-3 and 5,the scanning head is considered the integrated coating removal device.In the exemplary configuration in FIG. 4, the scanning head isconsidered the head component 310. A laser scanner is defined as thatportion of the scanning optics that enables realignment of the laserlight onto different positions of the surface. The laser scanner can beconfigured using one or more optical elements.

A first method of providing uniform removal of the coating includes acoating removal device configured with a single-axis laser scanner. FIG.6 illustrates a top down view of a simplified block diagram of ascanning head 100 including a single-axis laser scanner 104. Thesingle-axis laser scanner 104 is configured in this case to scan thelaser light along the x-axis on the surface, such as the surface 50(FIG. 1). An exemplary configuration of one such single-axis scanner isa reflecting scanner, such as the reflecting scanner 704 (FIG. 5),configured to pivot in one dimension, thereby scanning the laser lightalong a single-axis. The entire scanning head 100 moves along a secondaxis, in this case the y-axis. The scanning head 100 is configured tomove over the surface, in the y-axis, at a constant rate. FIG. 6 alsoshows the resulting scanning pattern on the surface 50 relative to thescanning head 100. FIG. 7 illustrates an expanded view of a portion ofthe scanning pattern shown in FIG. 6. FIG. 8 illustrates the position ofthe laser scanner 104 versus time. The position of the single-axis laserscanner 100 is a measure of the position of the laser light impingingthe surface as the single-axis scanner rotates back and forth. As shownin the scanning pattern of FIGS. 7 and 8, the scanning pattern does notprovide uniform coverage. In the center of the pattern, the lines areevenly spaced, but at the ends of the pattern, the lines are bunchedtogether. Such a pattern can be improved by moving the scanning head 100in steps as opposed to at a constant speed. However, the mass of thescanning head precludes the rapid accelerations required for start andstop motions. While the laser scanner 104 limits the width (x-dimension)of the scanning pattern, the length (y-dimension) is limited only by howfar the scanning head 100 can be moved. The scanning range of the laserscanner 104 is much less than the movement range of the scanning head100.

To solve the uniformity problem of the scanning head with onesingle-axis laser scanner, a second single-axis scanner is added to thescanning head. This second method of providing uniform removal of thecoating uses a coating removal device configured with two single-axislaser scanners. FIG. 9 illustrates a top down view of a simplified blockdiagram of a scanning head 200 including two single-axis laser scanners.A first single-axis laser scanner 206 is configured to scan the laserlight along a first direction, in this case the y-axis. A secondsingle-axis laser scanner 204 is configured to scan the laser lightalong a second direction, in this case along the x-axis. An exemplaryconfiguration of one such scanning head includes a first reflectingscanner, such as the reflecting scanner 706 (FIG. 5), configured topivot in one dimension, thereby scanning the laser light along a firstaxis, and a second reflecting scanner, such as the reflecting scanner704 (FIG. 5), configured to pivot in a second dimension, therebyscanning the laser light along a second axis. The entire scanning head200 is held motionless. The laser light is scanned in the two axis usingthe two laser scanners. FIG. 10 illustrates an expanded view of thescanning pattern performed by the scanning head 200 of FIG. 9. FIG. 11illustrates the position of the two laser scanners 204, 206 versus time.The position of the second laser scanner 204, which moves in this casein the x-direction, is the same as the single-axis laser scanner in FIG.6. The position of the first laser scanner 206, which moves in this casein the y-direction, is stationary until the second laser scanner changesdirection. The second method provides a scanning pattern with uniformspacing of the rows. The drawback of this configuration is that the scansize of the scanning pattern is limited in both axes by the range of thelaser scanners.

A third method of providing uniform removal of the coating uses acoating removal device that combines the advantage of the long scanningrange of the one single-axis scanning head with the uniformity of thetwo-single-head scanner head. FIG. 12 illustrates a top down view of asimplified block diagram of a scanning head 500 including twosingle-axis laser scanners. The scanning head 500 is configured to moveover the surface, in the y-axis, at a constant rate. FIG. 12 also showsthe resulting scanning pattern relative to the scanning head 500. Afirst single-axis laser scanner 506 is configured to scan the laserlight along a first direction, in this case along the x-axis. A secondsingle-axis laser scanner 504 is configured to scan the laser lightalong a second direction in a pattern similar to the second single-axislaser scanner 204 in FIG. 9. The first single-axis laser scanner 506functions similarly to the first single-axis laser scanner 206 of FIG. 9except that the movement patterns are different. FIG. 13 illustrates anexpanded view of a portion of the scanning pattern performed by thescanning head 500 of FIG. 12. FIG. 14 illustrates the position of thetwo laser scanners 504, 506 and scanning head 500 of FIG. 12 versustime. The position of the second single-axis laser scanner 504, whichmoves in this case in the x-direction, is the same as the secondsingle-axis laser scanner 204 in FIG. 9. Without the first single-axislaser scanner 506, the scanning pattern of the scanning head 500 in FIG.12 would be the same as the scanning pattern of the scanning head 100 inFIG. 6 because the scanning head 500 in FIG. 12 is also being moved inthe y-direction at a constant speed, as is shown in the third graph inFIG. 14. The position of the first single-axis laser scanner 506, whichmoves in this case in the y-direction, is used to offset the movement ofthe scanning head 500 in the y-direction. As shown in FIG. 14, themovement of the first single-axis laser scanner 506 is in the exactopposite direction as the movement of the scanning head 500, therebyresulting in a straight line scanning pattern in the x-direction. At theend of each scanning row, as indicated by each change of direction inthe x-position graph in FIG. 14, the first single-axis laser scanner 506is reset to its beginning position. The beginning position correspondsto the far left hand side of the y-position graph in FIG. 14. The bottomgraph in FIG. 14 shows the combination of the first single-axis laserscanner 506 and the scanning head 500.

The third method provides a scanning pattern with uniform spacing of therows in the x-direction, while also providing long scanning range in they-direction. The signal used to control the first single-axis laserscanner is generated by either an open-loop approach or a closed-loopapproach. In the open-loop approach, the scanning head speed, rowspacing, and scan time in the x-direction are known values. In theclosed loop-approach, feedback is provided where a position of thescanning head is determined and compared to a desired combinedy-position, such as the bottom graph in FIG. 14. The result is used togenerate a control signal for the movement of the first single-axislaser scanner.

In some embodiments, the coating removal apparatus is configured toremove coating to achieve a desired surface roughness. The surfaceroughness is measured in situ, in real-time as the coating removalprocess occurs. A roughness measuring laser source provides a laserlight to the surface, thereby generating laser specular reflection andscattered reflections. The magnitude of the reflections at variousangles are detected and measured. The measured results are used tocalculate the surface roughness.

FIG. 17 illustrates an exemplary application of a surface roughnessmeasuring scheme. A laser light 232 of suitable power and wavelengthimpinges on the surface in a region approximate to where the laserprocessing, such as the laser ablation/photoablation processes describedabove, is to occur. In some embodiments, the illuminators 18, 418described above are adapted to provide the laser light used to measurethe surface roughness. In other embodiments, a laser light sourceindependent of the illuminators 18, 418 provides the laser light 232used to measure the surface roughness. The angle of incidence θi of thelaser light 232 is the angle from the perpendicular to the surface 50 atthe position 52. The angle of incidence θi can be perpendicular to thesurface 50 or some other angle to the perpendicular. The primaryreflected light 234 is the specular reflection at the primary angle ofreflection θr, where the primary angle of reflection θr is equal to theangle of incidence θi. In some embodiments, the photodetector 20, 420described above is adapted to collect the reflected light at the primaryreflection angel θr. In other embodiments, a photodetector independentof the photodetector 20, 420 collects the primary reflected light 234 atthe primary reflection angle θr.

In addition to the primary reflected light 234, there are also scatteredreflections, such as reflected light 236-240, at other non-primaryreflection angles. The magnitude of the reflections at the variousangles is dependent on the surface roughness. By placing optical sensorsat a number of the various angles, a measurement of the reflected light234-240 is made. By suitable calculations, a measure of the surfaceroughness is derived using the measured reflected light 234-240 at thevarious angles. The calculated surface roughness can be used todetermine if subsequent laser light ablation is to be performed to alterthe measured surface roughness. The angles at which the non-primaryreflections occur are determined by the frequency of the laser lightused to measure the surface roughness and the angle of incidence θi, asis well known in the art. The number of non-primary reflection angles atwhich the scattered light is measured, and the correspondingphotosensitive detectors used to detect the scattered light at theseangles, is application specific according to the desired degree ofaccuracy of the measured surface roughness.

In some embodiments, the surface is composed of materials and/orstructures that infrared (IR) laser light merely passes through withoutthe desired effects. When the surface to be removed is composed of suchmaterials and/or structures, the coating removal apparatus includes anultraviolet (UV) laser system. For example, the laser source 12 (FIG. 1)and the laser source 412 (FIGS. 2, 3, 5), and the laser source 112 (FIG.4) are configured as UV laser sources.

The UV laser system is configured to provide an environmentally “green”composite surface treatment process that is inherently amenable toautomation. By directing UV laser light onto the composite substrate ina controlled manner, the surface can be cleaned, textured, and“chemically functionalized” in a highly selective and controlled manner.In contrast to IR laser light, UV laser light is readily absorbed in avery shallow outer layer of the composite surface. This allows the UVlaser to achieve a far higher degree of control in processing compositematerials.

The UV laser light interacts with the composite substrate surface insuch a manner as to create “photoablation” effects. Photoablation occurswhen the energy density of the incident laser light is sufficient tobreak the chemical bonds within the laser-illuminated spot on the targetsubstrate surface. The result is the vaporization of a small volume ofmaterial that emits from the surface as a gas or a low-temperatureplasma. In some embodiments, the gas that emits from thelaser-illuminated spot on the target substrate surface undergoes afluorescence reaction where the absorption of incident UV laser light inthe gas/plasma causes the emission of visible light, typically in thepurple-blue wavelengths in the approximate range of 375-475 nanometers.In some embodiments, the photodetectors, such as the photodetector 20 inFIG. 1, are configured as fluorescence sensor(s) that are used in twoways to control the UV laser process. First, the fluorescence sensor(s)senses the fluorescence emissions generated by the UV laser radiationilluminating the gas or plasma emitting from the photoablated area.Second, the fluorescence sensor(s) sense the fluorescence of thecomposite surface itself or the dyes or marking materials that can beapplied to the surface as a process control “marker”. This lattertechnique may rely on laser itself at a reduced power or a UVillumination means distinct from the laser. A typical embodiment wouldemploy UV-emitting LEDs for this purpose. In some embodiments, theilluminators used to provide light illumination to the surface, such asthe illuminators 18 in FIG. 1, are configured as secondary UV lightsources. In some embodiments, the fluorescence reaction is measured inreal-time in order to effect one variation of continuous closed-loopcontrol of the coating removal system.

With the use of a pulsed laser, the photoablation process is performedas a series of discrete photoablation events that correspond to theimpingement of individual laser pulses against the substrate surface.This process allows for very accurately controlled laser effects thatcan readily achieve consistent photoablation depths. In an exemplaryapplication, photoablation depths can be controlled with a resolution ofabout 1 to about 2 microns.

During operation of the UV laser system, very brief laser pulses aredirected against the substrate from a scanning head incorporating noveltechnology. In some embodiments, each laser pulse has a pulse width inthe range of femtoseconds (10⁻¹² seconds) to microseconds (10⁻⁶seconds). The laser output optics in the scanning head are configured toilluminate a small spot on the target substrate with each laser pulse.In some embodiments, the laser-illuminated spot is typically in therange of about 5 to about 500 microns in diameter. The scanningmechanism repositions the laser optics to an adjacent spot before thenext laser pulse is transmitted through the beam delivery system, asdescribed in detail above. In some embodiments, the scanning head isconfigured with closed-loop electronic laser control interlocks in orderto assure that the laser energy is uniformly applied to the substrate.Such exemplary configurations are included in the coating removalsystems of FIGS. 1-5. In some embodiments, the position of the scanninghead relative to the to the target substrate or work piece is measuredwith a position encoder and the control function is performed withdigital computer circuits. The position encoder can be comprised ofexisting devices such as a rotary encoder or an optical position sensor.

The laser scanning head is located at the end of the laser lightdelivery system. In some embodiments, the scanning head employs anoscillating galvanometer or rotary scanning mechanism to translate thelaser focal spot across the surface of the target substrate in acontrolled manner. In some embodiments, the laser generates pulserepetition rates in the range of about 5 KHz to about 500 KHz.

In this manner, the UV laser system generates an essentially uniformdeposition of UV laser energy on the substrate in the form of manylaser-illuminated spots. The scanning head executes a programmed rasterpattern that compensates for the motion of the scanning head andproduces a uniform deposition of laser energy on the composite substratesurface, for example the laser scanning head 500 in FIG. 12.

The UV laser system can be configured with several types of conventionalavailable UV lasers, including but not limited to excimer (gas) lasers,diode-pumped solid-state lasers, and fiber lasers. In the latter twocases, frequency tripling (third harmonic) is accomplished withnonlinear optical material in order to produce laser radiation in theutilized UV wavelengths. In the case of excimer lasers, severaldifferent wavelengths can be employed, including but not limited to 308nm (xenon chloride), 248 nm (krypton fluoride), and 193 nm (argonfluoride) types. The UV laser comprises a source of laser light that isfed into the laser light delivery system and then scanned onto thetarget substrate in a controlled manner by the scanning head. The typeof laser selected for a given application depends on a number oftechnical factors, including but not limited to power level, wavelength,pulse repetition rate, beam quality, and cost.

The UV laser system employs a pulsed UV laser to generate an in-situplasma of controlled chemistry at the laser-illuminated substratesurface. The laser-induced plasma causes beneficial changes in thechemical and physical characteristics of the substrate surface undercontrolled conditions. Laser process parameters, including energydensity delivered to the substrate, laser radiation wavelength, pulseenergy, pulse duration, pulse repetition rate, beam quality, and otherscan all be adjusted to produce the desired effects on the substratematerial.

The interaction of the UV laser light with the composite materialsimultaneously produces multiple effects: The photoablation of thecomposite surface with overlapping laser-illuminated spots generates atextured surface that enhances adhesive bond strength and coatingsadhesion. The UV laser energy vaporizes deleterious organiccontaminants, including mold release agents, on the composite surfacethus enhancing bond strength and coatings adhesion. The UV laser energybeneficially alters the “chemical functionalities” of the compositesurface, thus enhancing bond strength and coatings adhesion at themolecular level. The altered chemical functionalities include surfaceenergy, bond state, and molecular composition.

In some embodiments of the UV laser system, the laser effects areenhanced by the use of a gas flow that creates a controlled environmentat the substrate surface where the laser energy is directed. The typesof gases used for this purpose include but are not limited to nitrogen,oxygen, hydrogen, argon, and helium. Both reactive and non-reactivegases can be used, depending upon the specific surface effects that aredesired. In certain applications, controlled mixtures of gases are used.

Gas flow is directed to the substrate surface at what is referred to asa laser process zone. The introduction of gas flows into the laserprocess zone at the substrate surface is intended to control thechemical composition of the plasma that is generated when the UV laserpulses illuminate the substrate surface. By controlling the partialpressure of gaseous species in the laser process zone, the chemistry ofthe laser plasma is tailored to produce specific chemical functionalityeffects at the composite surface. These effects include but are notlimited to polymerization, non-polymerization, crosslinking polymerfragmentation, oxidation, gas incorporation, and surface energymodification. Chemical functionality effects, in turn, control materialproperties such as adhesion, surface friction, permeability, surfaceenergy (wettability and water repellency), surface conductivity,biocompatibility, and optical properties such as reflectance.

In some embodiments, the method of introduction of these gases into thelaser process zone is similar to inert gas shielding practices employedin gas tungsten arc welding (GTAW) and gas metal arc welding (GMAW)procedures per American Welding Society (AWS) methodology. Using such adynamic gas shielding technique, controlled gas flow is continuouslyintroduced as the laser scanning head moves across the target substrate.In this manner, a controlled gas atmosphere is maintained in the laserprocess zone at the substrate surface under the moving laser scanninghead. Waste gas and the resulting photoablated material are removed aswaste

FIG. 15 illustrates an exemplary block diagram of the coating removaldevice 10 of FIG. 1 including a gas flow delivery system. The gas flowdelivery system 28 is configured to provide a continuous gas flow to thelaser process zone across the target surface 50, and specifically overeach target position on the surface, such as the position 52. In someembodiments, the gas flow delivery system 28 is configured to operateaccording to a dynamic gas shielding technique.

Another embodiment of a gas-assisted UV laser system includes theintroduction of controlled gas compositions into a closed chamber inwhich the laser process is conducted. Such a configuration includes awork piece, such as a surface, positioned inside of a vessel containingthe specified gas atmosphere. The UV laser system acts on the work piecethrough one or more optical penetrations of the vessel wall(s). This issimilar to a “glove box” arc welding process where the gas shielding iscomprised of a controlled atmosphere within a closed vessel thatcontains the work piece or substrate. In some applications, a partialvacuum is employed to facilitate the introduction of the desired gasatmosphere into the vessel.

FIG. 16 illustrates an exemplary block diagram of the coating removaldevice 10 of FIG. 1 including a gas flow delivery system and controlledgas chamber. The gas flow delivery system 128 is configured to provide acontinuous gas flow to a vessel 130 via a gas transport tube 134. Achamber 132 is formed within the vessel 130, into which the gas flows,thereby generating a controlled laser process zone across the targetsurface 50, and specifically over each target position on the surface,such as the position 52. In some embodiments, the vessel 130 includesoptically transparent portions (not shwon) through which the lightillumination, the UV laser light, and the reflected light pass. In otherembodiments, the entire vessel 130 is optically transparent.

In some embodiments, the waste collector, such as the waste collector 26in FIGS. 15 and 16, is configured as a vacuum extraction system thatfunctions to remove vapor and particulate waste products that issue fromthe laser treated surface during processing. The vacuum system istypically configured with an annular extractor means that is integratedwith the laser scanning head. The vacuum extractor prevents thecondensation or re-deposition of vaporous or particulate waste productsback onto the laser-treated surfaces during processing. This is animportant element in preserving the cleanliness and surface propertiesof the as-treated surfaces following laser processing. The vacuumextraction system also serves to substantially prevent thelaser-generated waste products from contaminating the laser opticscontained in the scanning head, thus reducing the maintenance requiredfor continuous operation of the laser system in a manufacturingenvironment.

In some embodiments, the vacuum extraction system captures thelaser-generated vapor and particulate wastes in a high-efficiencyparticulate air (HEPA) filter. This vacuum extraction/filtration meansincorporated into the laser system provides significant advantages forthe laser process in terms of environmental impact. The UV laser processbreaks the chemical bonds between monomers and the cross-linking betweenlong-chain hydrocarbon molecules that are the bases of polymer andcomposite matrix materials. Accordingly, most of the solid materialremoved by the UV laser photoablation process is reduced to atomic,molecular, and monomer species within a fluorescent gas medium thatissues from the laser-illuminated area during the impingement of eachlaser pulse on the substrate surface. The remainder of the photoablatedmaterial is reduced to fine particulate. Since these waste products arecaptured efficiently by the HEPA filter, the laser process is inherentlyan environmentally “green” process in which the wastes represent only asmall mass-fraction of the total processed material volume and the wasteproducts can be sequestered as solids in a small filter element suitablefor conforming waste disposal practices.

An advantage of the coating removal system is the incorporation ofactive, closed-loop controls that modulate the output of the laser inreal time during operation of the system. The use of closed-loop lasercontrols entails active interrogation of the substrate surface atintervals that equal or approximate the pulse repetition rate of thelaser process. The sensors incorporated in the closed-loop controlsmeasure the physical properties of the laser interaction with thesubstrate and/or the physical properties of the laser-treated substratesurface in real time, thus providing an electronic feedback loop for thelaser control interlocks.

Another advantage of the coating removal system is the use of a pulsedUV laser to create an in-situ fluorescent gas or low-grade plasma at thelaser-illuminated substrate surface. The laser-induced gas or plasmacauses beneficial changes in the chemical and physical characteristicsof the substrate surface under controlled conditions. Owing to thepersistence of the fluorescent gas or plasma, it effectively acts on thesubstrate surface in a continuous manner owing to the high pulserepetition rates employed in the UV laser process that sustain thefluorescence reaction. The laser process parameters, including energydensity delivered to the substrate, laser radiation wavelength, pulseenergy, pulse duration, pulse repetition rate, beam quality, and otherscan all be adjusted to produce the desired effects on the substratematerial.

Although the gas-assisted UV laser system embodiments, are shown inFIGS. 15 and 16 as being configured within the coating removal device10, it is understood that the gas-assisted UV laser system can beconfigured within any coating removal device, including the coatingremoval devices 300, 400, and 700.

In some laser applications, for example applications designed forprocessing smaller parts or subassemblies, the laser beam deliverysystem is stationary and the target substrate is moved via a mechanicalmeans relative to the laser. In some embodiments, this type of lasersystem is configured with cabinet-type enclosures that facilitate theintroduction of controlled gas atmospheres in the laser process zone.

The optical paths of the various embodiments described above, includingthe laser light path, the light illumination path, and the color sensingpath, are for exemplary purposes only. It is understood that alternativeconfigurations, including various combinations and numbers ofconventional optical elements can be used to achieve the desiredfunctionalities of the coating removal device described above.

The present invention has been described in terms of specificembodiments incorporating details to facilitate the understanding of theprinciples of construction and operation of the invention. Suchreference herein to specific embodiments and details thereof is notintended to limit the scope of the claims appended hereto. It will beapparent to those skilled in the art that modifications may be made inthe embodiment chosen for illustration without departing from the spiritand scope of the invention.

1-11. (canceled)
 12. A method of removing a coating from a surface, the method comprising: a. provide a laser light to a scanning head; b. moving the scanning head in a first direction substantially parallel to the surface at a constant speed thereby applying a first scanning pattern component to the laser light; c. configuring a first single-axis laser scanner within the scanning head to align the laser light along the second direction thereby applying a second scanning pattern component to the laser light; d. configuring a second single-axis laser scanner within the scanning head to align the laser light along a second direction thereby applying a third scanning pattern component, wherein the second scanning pattern component is equal and opposite in magnitude to the first scanning pattern component during sequential periods of time; and e. directing the laser light onto the surface according to a uniform scanning pattern, wherein the uniform scanning pattern if formed according to the first scanning pattern component, the second scanning pattern component, and the third scanning pattern component.
 13. The method of claim 12 wherein the scanning pattern comprises a series of rows, each row oriented parallel to the second direction.
 14. The method of claim 13 further comprising configuring the first single-axis laser scanner to rotate within a first plane, wherein rotation within the first plane corresponds to movement of the laser light in the first direction on the surface.
 15. The method of claim 14 further comprising configuring the second single-axis laser scanner to rotate within a second plane, wherein rotation within the second plane corresponds to movement of the laser light in the second direction on the surface.
 16. The method of claim 15 further comprising configuring the first single-axis laser scanner to rotate a first amount in the first plane between each period of time, the first amount corresponds to a separation distance between each row.
 17. The method of claim 13 where each row within the series of rows is uniformly spaced from one another.
 18. The method of claim 12 wherein the first direction is perpendicular to the second direction.
 19. The method of claim 12 wherein the third scanning pattern component comprises a first repeating pattern of first moving in the positive second direction at a second constant speed for the period of time and second moving in the negative second direction at the second constant speed for the period of time.
 20. The method of claim 19 wherein the second scanning pattern component comprises a second repeating pattern of starting at a first position in the first direction, moving in the negative first direction at the constant speed for the period of time, and resetting to the first position.
 21. The method of claim 12 further comprising providing control signals to implement the first scanning pattern component, the second scanning pattern component, and the third scanning pattern component.
 22. A laser-based system to measure a surface roughness, the system comprising: a. a laser source to provide a laser light, wherein the laser source is aligned to direct the laser light onto a position on the surface at an angle of incidence; b. a plurality of photosensitive detectors each configured to receive light reflected from the surface as a result of the laser light impinging the position on the surface and to measure a magnitude of the reflected light received, wherein a first photosensitive detector is positioned at a primary angle of reflection and is configured to measure a primary specular reflected light, and each of a remaining number of photosensitive detectors is positioned at a non-primary angle of reflection and is configured to measure non-primary scattered reflected light; and c. a comparator coupled to each of the plurality of photosensitive detectors and configured to calculate a surface roughness of the surface according to the magnitude of reflected light measured at each of the plurality of photosensitive detectors.
 23. The system of claim 22 wherein the angle of incidence is equal to the primary angle of reflection.
 24. A method of measuring a surface roughness, the method comprising: a. providing a laser light; b. directing the laser light onto a position on the surface at an angle of incidence; c. positioning a plurality of photosensitive detectors, wherein a first photosensitive detector is positioned at a primary angle of reflection to receive specular reflected light from the surface as a result of the laser light impinging the position on the surface, and each of a remaining number of photosensitive detectors is positioned at a non-primary angle of reflection to receive non-primary scattered reflected light; d. measuring a magnitude of reflected light at each of the plurality of photosensitive detectors; and e. calculating a surface roughness of the surface according to the magnitude of reflected light measured at each of the plurality of photosensitive detectors.
 25. The method of claim 24 wherein the angle of incidence is equal to the primary angle of reflection. 26-44. (canceled)
 45. A method of removing a coating from a composite surface, the method comprising: a. providing an ultraviolet laser pulse; b. directing the ultraviolet laser pulse to the position on the composite surface; and c. ablating a portion of the composite surface at the position as plasma.
 46. The method of claim 45 further comprising providing a series of ultraviolet laser pulses and directing the series of ultraviolet laser pulses to various positions on the composite surface according to a scanning pattern.
 47. The method of claim 46 wherein the series of laser pulses generates a series of ablated portions of the composite surface, thereby forming a textured surface.
 48. The method of claim 45 wherein the composite surface comprises a fiber-reinforced polymer composite.
 49. The method of claim 45 wherein the portion of the composite surface is ablated to a depth with a resolution of about one micrometer to about two micrometers.
 50. The method of claim 45 further comprising providing a gas flow over the position on the composite surface prior to directing the ultraviolet pulse to the position.
 51. The method of claim 50 wherein the gas flow is provided at a continuous rate.
 52. The method of claim 50 wherein the gas flow comprises one of the group consisting of nitrogen, hydrogen, argon, helium, and any combination thereof.
 53. The method of claim 50 wherein the gas flow comprises one of the group consisting of reactive gases, non-reactive gases, and a combination of reactive gases and non-reactive gases.
 54. The method of claim 50 wherein a chemical composition of the plasma is determined according to a composition of the gas flow.
 55. The method of claim 50 wherein the gas flow is provided according to a dynamic gas shielding technique.
 56. The method of claim 50 further comprising enclosing the position on the composite surface within a closed chamber, and providing the gas flow into the closed chamber.
 57. The method of claim 56 further comprising providing an optically transparent path through the closed chamber such that the ultraviolet laser pulse passes therethrough.
 58. The method of claim 50 wherein ablating the portion of the composite surface vaporizes contaminants on the portion.
 59. The method of claim 50 wherein a combination of an ultraviolet laser energy of the ultraviolet laser pulse and the gas flow at the position on the composite surface alters a chemical characteristic of the composite surface at the position, wherein the chemical characteristic is one of the group consisting of surface energy, bond state, molecular composition, and any combination thereof. 60-76. (canceled) 